(1) Field of the Invention
The present invention relates to the exercise of control over the flow of fluids, particularly heated fluids, and especially to the venting of exhaust gases from furnaces such as those employed in the making of steel. More specifically, this invention is directed to valves for use in releasing pressurized hot gases from enclosures such as blast furnaces. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use as an evacuation or pressure relief valve for installation at the throat of a blast furnace. Such pressure relief valves conventionally comprise a valve member, actuated by a movable arm, which is provided with a sealing surface configured to cooperate with a valve seat which forms part of an exhaust gas conduit. Such pressure relief valves are associated with means for developing the power required for operating the valves and further include some form of displacement mechanism which couples the power developing means to the movable arm.
A typical pressure relief valve system suitable for employment in the environment of a pressurized furnace is shown schematically in U.S. Pat. No. 3,601,357. As disclosed in U.S. Pat. No. 3,601,357, the means for developing the power for operating the valve member comprises a hydraulic jack. The hydraulic jack is coupled to a plurality of hydro-elastic accumulators via a control system. In the patented apparatus, the hydraulic jack is directly connected, via its piston rod, to the valve member or to a pivot arm connected to the valve member. If employed to relieve pressure in the case of an explosion within the furnace, the valve member of the patented system will be opened in opposition to applied closing forces by the oppositely directed forces produced by a shock wave resulting from the explosion; the pressure applied to the valve member thus acting against and exceeding the hydro-elastic pressure of the hydraulic jack. If operated as a conventional pressure-relief valve, the state of the valve may be automatically varied through sensing the pressure of the gas in the furnace throat; signals commensurate with the sensed pressure being employed to control the operation of the hydraulic jack whereby the valve will be opened automatically if the furnace throat gas pressure rises to an abnormal level.
The valve systems as shown in U.S. Pat. No. 3,601,357 may also be employed to supply pressurized gas to pressure equalization chambers, such chambers comprising part of a furnace charging installation, during the furnace charging process.
The opening of valves of the type schematically depicted in U.S. Pat. No. 3,601,357, regardless of whether used for over-pressure protection or pressure equalization, requires the raising of the valve member to a certain height above the valve seat. If the valve is mounted at the termination of an evacuation or vent conduit, as is the case with valves employed for explosion-protection purposes and also with shut-down valves which are employed to ventilate a blast furnace when it is operating at a slow rate, the valve member could not previously have been completely removed from the fluid flow passage. This characteristic of prior pressure relief valves has proven to be a serious operational deficiency. For example, the inability to remove the valve member completely from alignment with the valve seat has made servicing, such as repair or replacement of parts subject to wear, quite difficult by limiting access to such parts. Also, the valve member and at least part of the displacement mechanism connected thereto have been exposed to the corrosive and erosive action of the hot, particle laden furnace throat gases when in the open position.
Previously proposed solutions to the problems briefly discussed above would have required the sacrifice of certain advantages incident to the use of hydraulic jacks to develop the power required for operating the valve. This diminishing of desirable characteristics would be particularly strongly felt in the case of valve systems of the type disclosed in aforementioned U.S. Pat. No. 3,601,357 which relied for operation on a hydro-elastic effect. In the design of a pressure relief valve operating system, wherein power for operating the valve member is supplied by a hydraulic jack, there must be a practical and acceptable ratio between the pressure required to maintain the valve in the closed position and that required for a closing action. Additionally, and this becomes a problem when it is desired to move the valve member through a sufficient distance so that it is completely out of the path of gases passing through the valve seat, the displacement of the piston of the hydraulic jack must be maintained within moderate limits in order to keep the consumption of hydraulic fluid within the desired limits.
There has previously been no pressure relief valve operating mechanism available which would enable the valve member to be moved completely from the path of gases being discharged through the valve seat with the aid of a hydraulic jack and wherein the valve operating system was characterized by a hydro-elastic system for controlling the operation of the jack.